A magnetic random access memory (MRAM) is a type of resistance change memory. Write methods of the MRAM are a magnetic field write method and spin transfer torque write method. The spin transfer torque write method has a property by which as the size of a magnetic material decreases, a spin transfer torque electric current required for magnetization switching reduces. This makes the spin transfer torque write method advantageous in increasing the degree of integration, decreasing the power consumption, and improving the performance.
An MTJ (Magnetic Tunnel Junction) element of the spin transfer torque write method has a multilayered structure including two ferromagnetic layers and a nonmagnetic barrier layer (thin insulating film) sandwiched between them, and stores digital data by the change in magnetic resistance caused by the spin polarization tunneling effect. The MTJ element can take a low-resistance state and high-resistance state in accordance with the magnetization arrangements in the two ferromagnetic layers. The MTJ element takes the low-resistance state when the magnetization arrangements (spin directions) in the two ferromagnetic layers are in a parallel state (P state), and the high-resistance state when the magnetization arrangements in the two ferromagnetic layers are in an antiparallel state (AP state).